Effects of fimbria lesions on trace two-way active avoidance acquisition and retention in rats

Revisiting the role of anxiety in the initial acquisition of two-way active avoidance: pharmacological, behavioural and neuroanatomical convergence

Two-way active avoidance (TWAA) acquisition constitutes a particular case of approach -avoidance conflict for laboratory rodents. The present article reviews behavioural, psychopharmacological and neuroanatomical evidence accumulated along more than fifty years that provides strong support to the contention that anxiety is critical in the transition from CS (conditioned stimulus)-induced freezing to escape/avoidance responses during the initial stages of TWAA acquisition. Thus, anxiolytic drugs of different types accelerate avoidance acquisition, anxiogenic drugs impair it, and avoidance during these initial acquisition stages is negatively associated with other typical measures of anxiety. In addition behavioural and developmental treatments that reduce or increase anxiety/stress respectively facilitate or impair TWAA acquisition. Finally, evidence for the regulation of TWAA acquisition by septo-hippocampal and amygdala-related mechanisms is discussed. Collectively, the reviewed evidence gives support to the initial acquisition of TWAA as a paradigm with considerable predictive and (in particular) construct validity as an approach-avoidance conflict-based rodent anxiety model.

Assessment of serotonergic system in formation of memory and learning

We evaluated the involvement of the serotonergic system on memory formation and learning processes in healthy adults Wistar rats. Fifty-seven rats of 5 groups had one serotonergic nuclei damaged by an electric current. Electrolytic lesion was carried out using a continuous current of 2mA during two seconds by stereotactic surgery. Animals were submitted to learning and memory tests. Rats presented different responses in the memory tests depending on the serotonergic nucleus involved. Both explicit and implicit memory may be affected after lesion although some groups showed significant difference and others did not. A damage in the serotonergic nucleus was able to cause impairment in the memory of Wistar. The formation of implicit and explicit memory is impaired after injury in some serotonergic nuclei.

Behavioral facilitation after hippocampal lesion: A review

When parts of the brain suffer from damage, certain functional deficits or impairments are the expected and typical outcome. A myriad of examples show such negative consequences, which afford the daily tasks of neurologists, neuropsychologists, and also behavioral neuroscientists working with experimental brain lesions. Compared to lesion-induced deficits, examples for functional enhancements or facilitation after brain lesions are rather rare and usually not well studied. Here, the mammalian hippocampus seems to provide an exception, since substantial evidence shows that its damage can have facilitatory behavioral effects under certain conditions. This review will address these effects and their possible mechanisms. It will show that facilitatory effects of hippocampal lesions, although mostly studied in rats, can be found in many mammalian species, that is, they are apparently not species-specific. Furthermore, they can be found with various lesion techniques, from tissue ablation, to neurotoxic damage, and from damage of hippocampal structure itself to damage of fiber systems innervating it. The major emphasis of this review, however, lies on the behavioral effects and their interpretations. Thus, facilitatory effects can be found in several learning paradigms, especially active avoidance, and some forms of Pavlovian and instrumental conditioning. These will be discussed in light of pertinent theories of hippocampal function, such as inhibition, spatial cognition, and multiple memory systems theories, which state that facilitatory effects of hippocampal lesions may reflect the loss of interference between hippocampal spatial and striatal procedural cognition. Using the example of the rat sequential reaction time task, it will also be discussed how such lesions can have direct and indirect consequences on certain behavioral readouts. A final note will advocate considering possible functional facilitation also in neurologic patients, especially those with hippocampal damage, since such a strategy might provide new avenues for therapeutic treatments.

Decoupling Actions from Consequences: Dorsal Hippocampal Lesions Facilitate Instrumental Performance, but Impair Behavioral Flexibility in Rats

The present study is part of a series of experiments, where we analyze why and how damage of the rat's dorsal hippocampus (dHC) can enhance performance in a sequential reaction time task (SRTT). In this task, sequences of distinct visual stimulus presentations are food-rewarded in a fixed-ratio-13-schedule. Our previous study (Busse and Schwarting, 2016) had shown that rats with lesions of the dHC show substantially shorter session times and post-reinforcement pauses (PRPs) than controls, which allows for more practice when daily training is kept constant. Since sequential behavior is based on instrumental performance, a sequential benefit might be secondary to that. In order to test this hypothesis in the present study, we performed two experiments, where pseudorandom rather than sequential stimulus presentation was used in rats with excitotoxic dorsal hippocampal lesions. Again, we found enhanced performance in the lesion-group in terms of shorter session times and PRPs. During the sessions we found that the lesion-group spent less time with non-instrumental behavior (i.e., grooming, sniffing, and rearing) after prolonged instrumental training. Also, such rats showed moderate evidence for an extinction impairment under devalued food reward conditions and significant deficits in a response-outcome (R-O)-discrimination task in comparison to a control-group. These findings suggest that facilitatory effects on instrumental performance after dorsal hippocampal lesions may be primarily a result of complex behavioral changes, i.e., reductions of behavioral flexibility and/or alterations in motivation, which then result in enhanced instrumental learning.

Behavior and the cholinergic parameters in olfactory bulbectomized female rodents: Difference between rats and mice

Olfactory bulbectomy (OBX) in rodents induces a wide spectrum of functional disturbances, including behavioral, neurochemical, and neuromorphological alterations. We have examined the effects of OBX on behavior and the parameters of the cholinergic system in female rats and mice. In rats, OBX resulted in the appearance of some depressive-like behavioral marks, such as the decreased sucrose consumption, hyperactivity, impaired short-term memory and anxiety-like behavioral features, such as shortened presence in the center of the open field arena or open arms of the elevated plus-maze and an enhancement of avoidance behavior. These behavioral abnormalities could be associated with disturbances in hippocampal function, this suggestion being supported by the presence of cellular changes in this brain structure. No effect of OBX on the number of cholinergic neurons in the medial septum-diagonal band as well as on the acetylcholine content and acetylcholinesterase activity in the septum, hippocampus, and neocortex could be detected. In contrast, in mice, OBX impaired spontaneous alternation behavior and decreased the number of cholinergic neurons in the medial septum-diagonal band. These data demonstrate that rats and mice differently respond to OBX, in particular, OBX does not significantly affect the cholinergic system in rats.

Hippocampus and two-way active avoidance conditioning: Contrasting effects of cytotoxic lesion and temporary inactivation

Hippocampal lesions tend to facilitate two-way active avoidance (2WAA) conditioning, where rats learn to cross to the opposite side of a conditioning chamber to avoid a tone-signaled footshock. This classical finding has been suggested to reflect that hippocampus-dependent place/context memory inhibits 2WAA (a crossing response to the opposite side is inhibited by the memory that this is the place where a shock was received on the previous trial). However, more recent research suggests other aspects of hippocampal function that may support 2WAA learning. More specifically, the ventral hippocampus has been shown to contribute to behavioral responses to aversive stimuli and to positively modulate the meso-accumbens dopamine system, whose activation has been implicated in 2WAA learning. Permanent hippocampal lesions may not reveal these contributions because, following complete and permanent loss of hippocampal output, other brain regions may mediate these processes or because deficits could be masked by lesion-induced extra-hippocampal changes, including an upregulation of accumbal dopamine transmission. Here, we re-examined the hippocampal role in 2WAA learning in Wistar rats, using permanent NMDA-induced neurotoxic lesions and temporary functional inhibition by muscimol or tetrodotoxin (TTX) infusion. Complete hippocampal lesions tended to facilitate 2WAA learning, whereas ventral (VH) or dorsal hippocampal (DH) lesions had no effect. In contrast, VH or DH muscimol or TTX infusions impaired 2WAA learning. Ventral infusions caused an immediate impairment, whereas after dorsal infusions rats showed intact 2WAA learning for 40-50 min, before a marked deficit emerged. These data show that functional inhibition of ventral hippocampus disrupts 2WAA learning, while the delayed impairment following dorsal infusions may reflect the time required for drug diffusion to ventral hippocampus. Overall, using temporary functional inhibition, our study shows that the ventral hippocampus contributes to 2WAA learning. Permanent lesions may not reveal these contributions due to functional compensation and extra-hippocampal lesion effects.

Developing a clinically relevant model of cognitive training after experimental traumatic brain injury

BACKGROUND

Following traumatic brain injury (TBI), clinical cognitive training paradigms harness implicit and explicit learning and memory systems to improve function; however, these systems are differentially affected by TBI, highlighting the need for an experimental TBI model that can test efficacy of cognitive training approaches.

OBJECTIVES

To develop a clinically relevant experimental cognitive training model using the Morris water maze (MWM) wherein training on implicitly learned task components was provided to improve behavioral performance post-TBI.

METHODS

Eighty-one adult male rats were divided by injury status (controlled cortical impact [CCI]/Sham), non-spatial cognitive training (CogTrained/No-CogTrained), and extra-maze cues (Cued/Non-Cued) during MWM testing. Platform latencies, thigmotaxis, and search strategies were assessed during MWM trials.

RESULTS

Cognitive training was associated with improved platform latencies, reduced thigmotaxis, and more effective search strategy use for Sham and CCI rats. In the Cued and Non-Cued MWM paradigm, there were no differences between CCI/CogTrained and Sham/No-CogTrained groups. During novel testing conditions, CogTrained groups applied implicitly learned knowledge/skills; however, sham-cued CogTrained/rats better incorporated extramaze cues into their search strategy than the CCI-Cued group. Cognitive training had no effects on contusion size or hippocampal cell survival.

CONCLUSIONS

The results provide evidence that CCI-CogTrained rats that learned the nonspatial components of the MWM task applied these skills during multiple conditions of the place-learning task, thereby mitigating cognitive deficits typically associated with this injury model. The results show that a systematic application of clinically relevant constructs associated with cognitive training paradigms can be used with experimental TBI to affect place learning.

Age-dependent decline in learning and memory performances of WAG/Rij rat model of absence epilepsy

Recent clinical studies revealed emotional and cognitive impairments associated with absence epilepsy. Preclinical research with genetic models of absence epilepsy however have primarily focused on dysfunctional emotional processes and paid relatively less attention to cognitive impairment. In order to bridge this gap, we investigated age-dependent changes in learning and memory performance, anxiety-like behavior, and locomotor activity of WAG/Rij rats (a valid model of generalized absence epilepsy) using passive avoidance, Morris water maze, elevated plus maze, and locomotor activity cage. We tested 5 month-old and 13 month-old WAG/Rij rats and compared their performance to age-matched Wistar rats. Results revealed a decline in emotional and spatial memory of WAG/Rij rats compared to age-matched Wistar rats only at 13 months of age. Importantly, there were no significant differences between WAG/Rij and Wistar rats in terms of anxiety-like behavior and locomotor activity at either age. Results pointed at age-dependent learning and memory deficits in the WAG/Rij rat model of absence epilepsy.

Effects of muscarinic receptor antagonism in the basolateral amygdala on two-way active avoidance

The aim of the present study was to investigate whether the blockade of muscarinic receptors (mRs) in the basolateral amygdala (BLA), which receives important cholinergic inputs related to avoidance learning, affects the consolidation of two-way active avoidance (TWAA). In Experiment 1, adult male Wistar rats were bilaterally infused with scopolamine (SCOP, 20 μg/site) or PBS (VEH) in the BLA immediately after a single 30-trial acquisition session. Twenty-four hours later, avoidance retention was tested in an identical session. Results indicated that scopolamine in the BLA did not affect TWAA performance measured by the number of avoidance responses. Experiment 2 was conducted to test whether such a negative outcome might be due to the occurrence of overtraining during acquisition, which may indeed have a protective effect against scopolamine-induced memory deficits. In this experiment, rats were infused with scopolamine in the BLA immediately after a brief 10-trial acquisition session and tested 24 h later in a 30-trial retention session. The SCOP group showed significantly more avoidances and inter-trial crossings in the retention session than the VEH rats. Together, these results reveal that mRs blockade in the BLA does not disrupt TWAA consolidation and may even enhance avoidance performance when infused after a low number of acquisition trials. Performance factors, such as locomotor activity in the shuttle-box, may account, at least in part, for the facilitative effects of muscarinic antagonism in the BLA.

Involvement of cyclin-dependent kinase-like 2 in cognitive function required for contextual and spatial learning in mice

Cyclin-dependent kinase-like 2 (Cdkl2) is a cdc2-related serine/threonine protein kinase that is postnatally expressed in various brain regions, including the cerebral cortex, entorhinal cortex, hippocampus, amygdala, and dorsal thalamus. The extremely high Cdkl2 expression in these regions suggests that it has a role in cognition and emotion. Recent genetic studies indicate that mutations of Cdkl family kinases are associated with neurodevelopmental and neuropsychiatric disorders in humans. To elucidate the physiologic role of Cdkl2, we behaviorally analyzed Cdkl2(LacZ/LacZ) mice lacking Cdkl2. Cdkl2(LacZ/LacZ) mice had reduced latencies to enter the dark compartment after electric footshock in an inhibitory avoidance task and attenuated contextual fear responses when exposed to mild training conditions. Hippocampal spatial learning in the Morris water maze was slightly anomalous with mice exhibiting an abnormal swimming pattern. The aversive response in a two-way avoidance task was slightly, but not significantly, enhanced. On the other hand, Cdkl2(LacZ/LacZ) mice did not exhibit altered sensitivity to aversive stimuli, such as electric footshock and heat, or deficits in the elevated plus maze or rotating rod test. These findings suggest that Cdkl2 is involved in cognitive function and provide in vivo evidence for the function of Cdkl family kinases expressed in terminally differentiated neurons in mice.

Learning processing in the basal ganglia: a mosaic of broken mirrors

In the present review we propose a model to explain the role of the basal ganglia in sensorimotor and cognitive functions based on a growing body of behavioural, anatomical, physiological, and neurochemical evidence accumulated over the last decades. This model proposes that the body and its surrounding environment are represented in the striatum in a fragmented and repeated way, like a mosaic consisting of the fragmented images of broken mirrors. Each fragment forms a functional unit representing articulated parts of the body with motion properties, objects of the environment which the subject can approach or manipulate, and locations the subject can move to. These units integrate the sensory properties and movements related to them. The repeated and widespread distribution of such units amplifies the combinatorial power of the associations among them. These associations depend on the phasic release of dopamine in the striatum triggered by the saliency of stimuli and will be reinforced by the rewarding consequences of the actions related to them. Dopamine permits synaptic plasticity in the corticostriatal synapses. The striatal units encoding the same stimulus/action send convergent projections to the internal segment of the globus pallidus (GPi) and to the substantia nigra pars reticulata (SNr) that stimulate or hold the action through a thalamus-frontal cortex pathway. According to this model, this is how the basal ganglia select actions based on environmental stimuli and store adaptive associations as nondeclarative memories such as motor skills, habits, and memories formed by Pavlovian and instrumental conditioning.

Effects of parafascicular excitotoxic lesions on two-way active avoidance and odor-discrimination

To investigate whether the parafascicular (PF) nucleus of the thalamus is involved in different learning and memory tasks, two experiments were carried out in adult male Wistar rats that were submitted to pre-training bilateral N-methyl-d-aspartate PF infusions (0.15M, pH 7.4; 1.2 microl/side, 0.2 microl/min). In Experiment 1, we evaluated the effects of PF lesions in two identical 30-trial training sessions, separated by a 24-h interval, of a two-way active avoidance conditioning. PF-lesioned rats exhibited impaired performance in both sessions, measured by number of avoidance responses. In Experiment 2, the effects of PF lesions were assessed in a training session (5 trials) and a 24-h retention test (2 retention trials and 2 relearning trials) of an odor-discrimination task. PF lesions did not significantly disrupt the acquisition or the first retention trial, which was not rewarded. However, lesioned animals' performance was clearly affected in subsequent trials, following the introduction of the single non-rewarded trial. Current data are discussed considering evidence that lesions of the PF nucleus affect learning and memory functions mediated by anatomically related areas of the frontal cortex and striatum.

Alleviation of the effects of endotoxin exposure on behavior and hippocampal IL-1beta by a selective non-peptide antagonist of corticotropin-releasing factor receptors

Previous research has shown that lipopolysaccharide (LPS) or interleukin-1beta (IL-1beta) administration produces learning/memory deficits in a variety of paradigms. In our laboratory, we have consistently observed LPS-induced behavioral alterations in a two-way active avoidance conditioning paradigm. Following LPS administration, one factor that affects cytokine production is corticotropin-releasing factor (CRF). CRF has well known anti-inflammatory effects, via stimulation of ACTH and corticosterone release. However, CRF acting directly on immune cells or within the CNS may potentiate proinflammatory effects. The current experiments explored the potential of antalarmin, a CRF-R1 non-peptide antagonist, to diminish or negate deficits observed with LPS administration. On the first day of testing, four-month-old male C57BL/6J mice received an intraperitoneal (i.p.) injection of antalarmin, followed 90min later by a second i.p. injection of LPS 4h prior to two-way active avoidance conditioning testing. As hypothesized, LPS administration altered performance. However, pretreatment with antalarmin attenuated the adverse effects of LPS administration. Moreover, evidence indicates that antalarmin attenuated hippocampal, but not peripheral, cytokine release. The behavioral results cannot be explained by alterations in the HPA axis, as antalarmin did not affect the LPS-induced rise in corticosterone. The current research contributes preliminary evidence that CRF may be an important factor in the development of LPS-induced behavioral effects, and that blocking the activity of CRF may be sufficient to alleviate some of the effects of endotoxin exposure, possibly due to diminished LPS-induced IL-1beta release in the dorsal hippocampus.

Hippocampal infusions of pyruvate reverse the memory-impairing effects of septal muscimol infusions

Hippocampal infusions of glucose reverse memory deficits in spontaneous alternation and in a continuous multiple trial inhibitory avoidance task. The current experiments tested whether glucose metabolism may participate in these effects of glucose. Specifically, these experiments determined whether the glycolytic metabolite pyruvate would mimic these effects of glucose. Male Sprague-Dawley rats were given septal infusions of vehicle or the gamma-aminobutyric acid (GABA) receptor agonist muscimol (0.15 nmol for spontaneous alternation or 5 nmol for continuous multiple trial inhibitory avoidance) combined with hippocampal infusions of vehicle or pyruvate (200 nmol) 15 min prior to assessing spontaneous alternation or training in a continuous multiple trial inhibitory avoidance task. The infusions of muscimol decreased percent alternation scores and continuous multiple trial inhibitory avoidance retention latencies tested 48 h after training. More importantly, hippocampal infusions of pyruvate reversed the deficits produced by septal infusions of muscimol on both tasks. These findings show for the first time that hippocampal infusions of pyruvate influence memory and suggest that glucose may affect memory via glycolytic metabolism.

Postnatal Development of Conditioned Reflex Behavior: Comparison of the Times of Maturation of Plastic Processes in the Rat Hippocampus

The formation of conditioned reflex fear, escape responses, and conditioned avoidance responses during acquisition of a conditioned two-way avoidance reflex was studied in rats of different ages. Rats aged 16-17 days acquired the conditioned reflex but not the escape reaction or the conditioned avoidance response; acquisition efficiency was higher than in adult rats. Escape responses appeared from postnatal day 18. The ability to acquire this type of learning was complete by age 3-4 weeks. Maturation of the mechanisms of the "classical" (the fear phase) and operant (transfer to another sector in response to the unconditioned stimulus) components did not facilitate acquisition of the conditioned two-way avoidance reflex until the middle of postnatal week 4. Learning efficiency in four-week-old rats was lower than in adults. It is suggested that the maturation of different types of memory may be associated with the periods at which plastic processes develop in the hippocampus.

Peripheral lipopolysaccharide administration impairs two-way active avoidance conditioning in C57BL/6J mice

Peripheral administration of lipopolysaccharide (LPS) or interleukin-1 (IL-1) may lead to alterations of CNS function and behavioral changes designated "sickness behavior." Further, some experiments show evidence of LPS- and cytokine-mediated alterations in learning and memory. The current series of experiments examined the effects of a single or repeated intraperitoneal LPS injections, at a number of doses and time points before or after test sessions, on behavior in a two-way active avoidance conditioning paradigm. Subjects were able to avoid the mild shock stimulus, escape it, or fail to respond to it. Subjects treated with LPS at many, but not all, of the time points sampled showed impaired learning, by exhibiting significantly fewer avoidance responses than controls. Furthermore, an LPS-induced increase in non-cued inter-trial interval crossings was observed during the later days of testing, suggesting that a greater percentage of their avoidance responses was not conditioned and their behavior was less efficient. Taken together, the results suggest that LPS-treated animals showed a diminished association between conditioned stimulus (CS) and unconditioned stimulus (US). These results support the theory that peripheral immune stimuli may induce deleterious effects on learning, and extend the work to a negatively reinforced operant procedure.

Effects of active shock avoidance learning on hippocampal neurogenesis and plasma levels of corticosterone

Hippocampal granule neurons that are newly formed during adulthood might be involved in learning and memory processes. Experimental data suggest that only hippocampus-dependent learning tasks stimulate neurogenesis. To further address this issue, the effects of active shock avoidance (ASA) learning on hippocampal progenitor proliferation and survival of newly formed cells were investigated. ASA training, although considered as hippocampus-independent, is known to induce several neurobiological alterations in the hippocampus. Adult Wistar rats were trained in a shuttle box using a 1-day or 4-day paradigm and brains were analyzed for the mitotic marker Ki-67. Effects on survival of newly generated cells were examined by immunocytochemistry for 5-bromo-2-deoxyuridine (BrdU), which was injected 1 week before the training. Neither proliferation nor survival was affected by the ASA learning task. Because elevated glucocorticoid levels have a negative impact on hippocampal neurogenesis, blood samples were taken throughout the 4-day training paradigm. Both trained animals and control rats that were only placed in the shuttle box without receiving foot shocks showed a similar rise in corticosterone, enabling us to exclusively investigate the effects of ASA learning on neurogenesis without differential interference of stress between groups. On the other hand, the finding that ASA induced elevations in plasma corticosterone, but did not influence proliferation or survival of newly formed cells, indicates that this type of stress does not affect neurogenesis. The present study shows that, in line with the existing data on other hippocampus-independent learning tasks, ASA training has no effect on hippocampal neurogenesis.

Central administration of a caspase inhibitor impairs shuttle-box performance in rats

Recent studies suggest that caspase-3-mediated mechanisms are essential for neuronal plasticity. N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val- Asp(OMe)-fluoromethyl ketone (z-DEVD-fmk), a caspase inhibitor with predominant specificity toward caspase-3, has been shown to block long-term potentiation in hippocampal slices. Intrahippocampal infusion of a caspase-3 inhibitor to rats has been shown to significantly impair spatial memory in the water maze. The present work was designed to study whether i.c.v. administration of a caspase-3 inhibitor z-DEVD-fmk impairs learning in other tasks related to specific forms of memory in rats. The rats received bilateral injections of z-DEVD-fmk or N-benzyloxycarbonyl-Phe-Ala-fluoromethyl ketone (z-FA-fmk) ("control" peptide) at a dose of 3 nmol. Administration of z-DEVD-fmk significantly decreased the number of avoidance reactions in some blocks of trials in the active avoidance (shuttle box) learning, while z-FA-fmk had no effect as compared with intact rats. However, only a slight effect of the caspase inhibitor across the session was found. z-DEVD-fmk impaired development of some essential components of the two-way active avoidance performance, such as escape reaction, conditioned fear reaction, and inter-trial crossings. Measurement of caspase-3 activity in rat brain regions involved in active avoidance learning revealed most expressed z-DEVD-fmk-related inhibition of the enzyme activity (about 30%) in the fronto-parietal cortex. A similar effect was close to significant in the hippocampus, but not in the other cerebral structures studied. In primary cultures of cerebellar neurons z-DEVD-fmk (2-50 microM) inhibited caspase-3 activity by 60-87%. We suggest that moderate inhibition of caspase-3 resulting from the central administration of z-DEVD-fmk to rats may impair active avoidance learning. Taking into account previous data on the involvement of neuronal caspase-3 in neuroplasticity phenomena we assume that the enzyme may be important for selected forms of learning.

Avoidance response in goldfish: emotional and temporal involvement of medial and lateral telencephalic pallium

The hippocampus and the amygdala are involved in avoidance learning in mammals. The medial and lateral pallia of actinopterygian fish have been proposed as homologous to the mammalian pallial amygdala and hippocampus, respectively, on the basis of neuroanatomical findings. This work was aimed at studying the effects of ablation of the medial telencephalic pallia (MP) and lateral telencephalic pallia (LP) in goldfish on the retention of a conditioned avoidance response previously acquired in two experimental conditions. In the first experiment, fish were trained in nontrace avoidance conditioning. In the second experiment, fish were trained in trace avoidance conditioning in which temporal cues were crucial for the learning process. An MP lesion affected the retention of the avoidance response in both procedures; in contrast, an LP lesion impaired the retention only in the trace-conditioning procedure. These data support the presence of two different systems of memory in fish, based on discrete telencephalic areas: the MP, involved in an emotional memory system; and the LP, involved in a spatial, relational, or temporal memory system. Moreover, these differential effects were similar to those produced by amygdalar and hippocampal lesions in mammals. We conclude that these specialized systems of memory could have appeared early during phylogenesis and could have been conserved throughout vertebrate evolution.

The influence of midazolam on active avoidance retrieval and acquisition rate in rats

The purpose of the present study was to examine the influence of midazolam on the retrieval and acquisition rate of two-way active avoidance in rats. In the schedule 2 x 100 trials, the effects of midazolam (0.5-5.0 mg/kg), benzodiazepine binding site antagonist flumazenil (2.5-10.0 mg/kg), specific antagonist of GABA(A) receptor, bicuculline (0.5-4.0 mg/kg), and the blocker of GABA(A) receptor containing Cl(-) channels, picrotoxin (1.0-5.0 mg/kg), on the second day retrieval of avoidance performance were investigated, as well as the influence of the used blockers of GABA(A) receptor function on midazolam effects. Furthermore, the effect of midazolam (1.0 mg/kg) on acquisition rate in the 5 x 50 schedule, as well as the effects of third day treatment changing in that paradigm, was examined. Throughout the study, drugs were given intraperitoneally, 30 min before testing. Midazolam at the dose of 1.0 mg/kg facilitated avoidance retrieval, whereas flumazenil and bicuculline did not significantly change behavior. Picrotoxin (5.0 mg/kg) diminished performance. All three kinds of blockers used abolished facilitatory action of midazolam, confirming GABAergic mediation of the effect of benzodiazepine. Midazolam (1.0 mg/kg) increased acquisition rate during five consecutive days relative to saline, but without significant effect on the first day acquisition. In the case of third day changing of treatments, the intersection of regression rate lines was detected. Results from active avoidance paradigm experimentally support the findings from human studies that in certain circumstances, benzodiazepines, potentiating GABAergic neurotransmission, could produce retrieval-enhancing effects in memory tasks.

Improvement of shuttle-box performance by anterodorsal medial septal lesions in rats

Septal lesions impair a variety of tasks, including inhibitory avoidance and one way active avoidance. In contrast, these lesions improve two-way active avoidance, probably by reducing anxiety. The present work aimed to study whether anterodorsal medial septal lesion (a) improves performance of two-way active avoidance task (Experiment I), as it has been observed with wider septal lesion, and (b) affect anxiety and/or locomotor activity (Experiment II). This precise region was chosen because some evidences suggest that its lesion do not lead to a reduction of anxiety. Lesioned rats tended to make a higher, but statistically non-significant (P=0.074), number of avoidances regardless of the session, being this difference statistically significant on the retention session (RT). The same lesion did not appear to have an anxiolytic effect, and did not affected basal locomotor activity. Different possible explanations of our results are discussed.